U.S. patent number 4,065,935 [Application Number 05/705,933] was granted by the patent office on 1978-01-03 for articulated joints for deep water installations.
This patent grant is currently assigned to Taylor Woodrow Construction Limited. Invention is credited to Reginald Edward Dowton Burrow, David Edmund Plaskitt.
United States Patent |
4,065,935 |
Burrow , et al. |
January 3, 1978 |
Articulated joints for deep water installations
Abstract
An articulated joint for a deep water installation in which two
structural members are connected by replaceable flexible tendons to
which there is access from one of the structural members to permit
a pressure bottle to be fitted for receiving for replacement any
selected one of the tendons after release of this tendon from the
other structural member.
Inventors: |
Burrow; Reginald Edward Dowton
(Hatch End, EN), Plaskitt; David Edmund (High
Wycombe, EN) |
Assignee: |
Taylor Woodrow Construction
Limited (EN)
|
Family
ID: |
10305628 |
Appl.
No.: |
05/705,933 |
Filed: |
July 16, 1976 |
Foreign Application Priority Data
|
|
|
|
|
Jul 18, 1975 [UK] |
|
|
30310/75 |
|
Current U.S.
Class: |
405/202; 405/207;
405/210; 52/223.4 |
Current CPC
Class: |
E21B
43/017 (20130101); F16L 27/026 (20130101); F16L
27/06 (20130101); F16L 27/10 (20130101) |
Current International
Class: |
E21B
43/00 (20060101); E21B 43/017 (20060101); F16L
27/00 (20060101); F16L 27/06 (20060101); F16L
27/02 (20060101); F16L 27/10 (20060101); E02D
021/00 () |
Field of
Search: |
;61/95,101,87,69K,94
;175/7,8 ;166/.5,.6 ;9/8R ;52/230 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shapiro; Jacob
Attorney, Agent or Firm: Armstrong, Nikaido &
Marmelstein
Claims
We claim:
1. An articulated joint for a deep water installation in which two
structural members are connected so as to afford limited pivotal
movement between the members, the joint comprising replaceable
flexible tendons connecting the structural members with a clearance
between the members, each said tendon terminating at each end in a
cylindrical member that is entered, at a mounting station
associated with the relevant structural member, in a tubular
portion of a tendon anchorage, there being access from the interior
of each of the structural members to that end of each of said
tendons that is connected to this structural member; each said
tendon being releasably engaged at one end in its anchorage in one
structural member, disposed in fluid-tight manner with respect to
this structural member, the mounting station for each tendon is
this structural member being adapted to have fitted at it a
pressure bottle for containing the tendon whilst maintaining the
fluid-tight sealing relationship of the tendon with the structural
member, and each said tendon being held releasably fast with
respect to said other structural member by a screw-threaded member
mounted on said cylindrical member at the other end of the tendon;
removal of the tendon from the joint being effected, with the
pressure bottle fitted and the tendon released at its other end
from the other structural member by removing said screw threaded
member, by pressurizing the bottle, releasing said one end of the
tendon, and depressurizing the bottle to permit the tendon to enter
the bottle; there being a tendon extension at the other end of the
tendon which is arranged to enter into fluid-tight sealing
relationship with the last-mentioned structural member, when entry
of the tendon into the pressure bottle is completed, thereby
permitting removal of the tendon and the bottle from the tendon
extension and fitting of a replacement tendon to the tendon
extension.
2. A joint as claimed in claim 1, wherein each mounting station at
which said other end of each tendon is releasably held fast with
respect to said other structural member is adapted to have fitted
to it after release of the tendon a sealing cap that serves to
maintain said other structural member fluid-tight during
replacement of the tendon.
3. A joint as claimed in claim 1, wherein the cylindrical member at
said one end of each tendon, and the cylindrical member and the
screw-threaded member at said other end of the tendon are normally
enclosed by sealing domes that are removed to permit fitting of
said tendon extension, a sealing cap to contain said tendon
extension, and said pressure bottle.
4. A joint as claimed in claim 3, wherein said sealing cap can be
pressurized to assist removal of the tendon.
5. An articulated joint for a deep water installation in which two
structural members are connected so as to afford limited pivotal
movement between the members, the joint comprising replaceable
flexible tendons connecting the structural members with a clearance
between the members, each said tendon terminating at each end in a
cylindrical member that is entered, at a mounting station
associated with the relevant structural member, in a tubular
portion of a tendon anchorage there being access from the interior
of one only of the structural members to that end of each of said
tendons that is connected to this structural member and each said
tendon being releasably held fast at this end by a screw-threaded
member mounted on said cylindrical member at this end of the
tension, disposed in fluid-tight manner with respect to this
structural member, the mounting station for each tendon in this
structural member being adapted to have fitted at it a pressure
bottle for containing the tendon whilst maintaining the fluid-tight
sealing relationship of the tendon with the structural member; and
each tendon at its other end being made releasably fast with the
other of the structural members by the engagement of an anchor head
carried by the tendon with an anchor block fast with the other
structural member, this engagement being effected or released by
actuation of a drive connected thereto that passes along the tendon
from said one only of the structural members; removal of the tendon
from the joint being effected, with the pressure bottle fitted and
the tendon released at its other end from the other structural
member by actuating said drive member, by pressurizing the bottle,
releasing said one end of the tendon, and depressurizing the bottle
to permit the tendon to enter the bottle; there being a tendon
extension at the other end of the tendon which is arranged to enter
into fluid-tight sealing relationship with the last-mentioned
structural member, when entry of the tendon into the pressure
bottle is completed, thereby permitting removal of the tendon and
the bottle from the tendon extension and fitting of a replacement
tendon to the tendon extension.
6. A joint as claimed in claim 5, wherein the anchor head engages
in screw-threaded manner with the anchor block; wherein said drive
includes a flexible drive shaft passed through a bore in the tendon
to engage the anchor head in rotationally fast manner; and wherein
resiliently-loaded locking means are provided in the region of the
anchor block and anchor head for locking the tendon against
rotation during actuation of the drive.
7. A joint as claimed in claim 5, wherein the anchor head engages
in screw-threaded manner with the anchor block; wherein said drive
includes a bore in the tendon and a hydraulic motor actuable by
hydraulic fluid passed along this bore and coupled for effecting or
releasing the engagement of the anchor head and anchor block; and
wherein resiliently-loaded locking means are provided in the region
of the anchor block and anchor head for locking the tendon against
rotation during actuation of the drive.
8. An articulated joint for a deep water installation in which two
structural members are connected so as to afford limited pivotal
movement between the members, the joint comprising replaceable
flexible tendons connecting the structural members with a clearance
between the members, each said tendon terminating at each end in a
cylindrical member that is entered, at a mounting station
associated with the relevant structural member, in a tubular
portion of a tendon anchorage there being access from the interior
of one only of the structural members to that end of each of said
tendons that is connected to this structural member and each said
tendon being releasably held fast at this end by a screw-threaded
member mounted on said cylindrical member at this end of the
tendon, disposed in fluid-tight manner with respect to this
structural member, the mounting station for each tendon in this
structural member being adapted to have fitted at it a pressure
bottle for containing the tendon whilst maintaining the fluid-tight
sealing relationship of the tendon with the structural member; and
each tendon at its other end being made releasably fast with the
other of the structural members by the engagement of an anchor head
carried by the tendon with an anchor block fast with the other
structural member; this engagement being effected or released by
rotating the entire tendon; removal of the tendon from the joint
being effected, with the pressure bottle fitted and the tendon
released at its other end from the other structural member by
rotating the entire tendon, by pressurizing the bottle, releasing
said one end of the tendon, and depressurizing the bottle to permit
the tendon to enter the bottle; there being a tendon extension at
the other end of the tendon which is arranged to enter into
fluid-tight sealing relationship with the last-mentioned structural
member, when entry of the tendon into the pressure bottle is
completed, thereby permitting removal of the tendon and the bottle
from the tendon extension and fitting of a replacement tendon to
the tendon extension.
9. An articulated joint for a deep water installation in which two
structural members are connected so as to afford limited pivotal
movement between the members, the joint comprising replaceable
flexible tendons connecting the structural members with a clearance
between the members, each said tendon terminating at each end in a
cylindrical member that is entered, at a mounting station
associated with the relevant structural member, in a tubular
portion of a tendon anchorage there being access from the interior
of one only of the structural members to that end of each of said
tendons that is connected to this structural member and each said
tendon being releasably held fast at this end by a screw-threaded
member mounted on said cylindrical member at this end of the
tendon, disposed in fluid-tight manner with respect to this
structural member, the mounting station for each tendon in this
structural member being adapted to have fitted at it a pressure
bottle for containing the tendon whilst maintaining the fluid-tight
sealing relationship of the tendon with the structural member; and
each tendon at its other end being made releasably fast with the
other of the structural members by the engagement of
resiliently-loaded keys with a key way; this engagement being
released by the actuation of ram means operated by supplying
pressure flud through a bore in the tendon; removal of the tendon
from the joint being effected, with the pressure bottle fitted and
the tendon released at its other end from the other structural
member by actuating said ram means by pressurizing the bottle,
releasing said one end of the tendon, and depressurizing the bottle
to permit the tendon to enter the bottle; there being a tendon
extension at the other end of the tendon which is arranged to enter
into fluid-tight sealing relationship with the last-mentioned
structural member, when entry of the tendon into the pressure
bottle is completed, thereby permitting removal of thetendon and
the bottle from the tendon extension and fitting of a replacement
tendon to the tendon extension.
10. An articulated joint for a deep water installation in which two
structural members are connected so as to afford limited pivotal
movement between the members, the joint comprising replaceable
flexible tendons connecting the structural members with a clearance
between the members, each said tendon terminating at each end in a
cylindrical member that is entered, at a mounting station
associated with the relevant structural member, in a tubular
portion of a tendon anchorage there being access from the interior
of one only of the structural members to that end of each of said
tendons that is connected to this structural member and each said
tendon being releasably held fast at this end by a screw-threaded
member mounted on said cylindrical member at this end of the
tendon, disposed in fluid-tight manner with respect to this
structural member at a mounting station adapted to have fitted at
it a pressure bottle for containing the tendon whilst maintaining
the fluid-tight sealing relationship of the tendon with the
structural member; the other end of the tendon being made
releasably fast with the other of the structural members by the
engagement of resiliently-loaded arms with a key way; there being a
tendon extension at this other end formed as a cap that can engage
the arms to overcome their resilient-loading and hold them clear of
said key way; this cap being actuated by supplying pressure fluid
through a bore in the tendon; removal of the tendon from the joint
being effected, with the pressure bottle fitted and the tendon
released at its other end from the other structural member by
actuating said cab to engage said arms, by pressurizing the bottle,
releasing said one end of the tendon, and depressurizing the bottle
to permit the tendon to enter the bottle; said tendon extension at
the other end of the tendon being arranged to enter into
fluid-tight sealing relationship with the last-mentioned structural
member, when entry of the tendon into the pressure bottle is
completed, thereby permitting removal of the tendon and the bottle
from the tendon extension and fitting of a replacement tendon to
the tendon extension.
11. A joint as claimed in claim 10, wherein a locking means is
provided for locking said tendon extension in the position in which
it is in fluid-tight sealing relationship with said one of the
structural members.
12. A joint as claimed in claim 10, wherein washers are disposed in
abutting relationship along the tendon, the washers being of I
section and viewed on a radial plane having convex inner and outer
peripheral surfaces.
13. A joint as claimed in claim 12, wherein neighboring washers
have inter-engaging male and female shear plates.
Description
This invention relates to articulated joints for use in connecting
structures in installations for the extraction of oil and gas from
deep water sites such as the edges of continental shelves and
slopes, and is particularly concerned with such a joint in which
two structural members are connected by replaceable flexible
tendons.
The invention provides an articulated joint for a deep water
installation in which two structural members are connected so as to
afford limited pivotal movement between the members, the joint
comprising replaceable flexible tendons connecting the structural
members with a clearance between the members, there being access
from the interior of at least one of the structural members to that
end of each of said tendons that is connected to this structural
member and each said tendon being releasably held fast at this end
in fluid-tight manner with respect to this structural member at a
mounting station adapted to have fitted at it a pressure bottle for
containing the tendon whilst maintaining the fluid-tight sealing
relationship of the tendon with the structural member, whereby
removal of the tendon from the joint can be effected, with the
pressure bottle fitted and the tendon released at its other end
from the other structural member, by pressurizing the bottle,
releasing said one end of the tendon, and de-pressurizing the
bottle to permit the tendon to enter the bottle; there being a
tendon extension at the other end of the tendon which is arranged
to enter into fluid-tight sealing relationship with the
last-mentioned structural member, when entry of the tendon into the
pressure bottle is completed, thereby permitting removal of the
tendon and the bottle from the tendon extension and fitting of a
replacement tendon to the tendon extension.
For a better understanding of the invention and to show how the
same may be carried into effect, reference will now be made, by way
of example, to the accompanying drawings, in which:
FIG. 1 illustrates in diagrammatic sectional side view an assembly
consisting of a foundation member shown placed on the sea bed and
an upright column pivotably connected by a joint to the foundation
member and supporting above the surface of the sea a deck
superstructure,
FIG. 2 is a diagrammatic sectional view of the lower part of a
further form of an assembly such as shown in FIG. 1, drawn to a
larger scale than FIG. 1, and taken on the line B--B of FIG. 2,
FIG. 3 is a partly sectioned plan view of the part shown in FIG.
2.
FIG. 4 is a view similar to FIG. 2 but of a further modified
form,
FIG. 5 is a sectional view showing a tendon and its anchorages of a
joint such as provided in the assemblies of FIGS. 1 to 4,
FIG. 6 is a sectional view of the detail encircled at C in FIG. 5,
drawn to a larger scale and illustrating two operating
conditions,
FIG. 7 is a half cross-sectional view taken on the line D--D of
FIG. 6.
FIG. 8 is a view similar to FIG. 5 but illustrating a different
operating condition,
FIG. 9 is a sectional view showing protective members that can be
provided for the tendon of FIGS. 5 to 8,
FIG. 10 is a side view of a detail of the protective members of
FIG. 9 taken at E of FIG. 9 and drawn to a larger scale,
FIG. 11 is a section taken on the line F--F of FIG. 10,
FIG. 12 is a view similar to FIG. 5 of an alternative form,
FIGS. 13 to 16 are sectional views of the details respectively
encircled at G, H/I, and J in FIG. 12, drawn to a larger scale and
illustrating different operative conditions,
FIG. 17 is a sectional view on the line K--K of FIG. 15,
FIG. 18 is a sectional view on the line L--L of FIG. 13,
FIG. 19 shows in end and side view a detail of a modification of
the alternative form of FIGS. 12 to 18,
FIGS. 20 and 21 are sectional side views of two further alternative
forms, and
FIGS. 22 and 23 are sectional end views respectively taken on the
lines M--M and N--N of FIGS. 20 and 21.
The foundation member 1 is in the form of a housing for housing
so-called"subsea completions", the member 1 being a prestressed
concrete member which is constructed to have adequate buoyancy and
stability for towing from its place of construction to its intended
offshore location, where it is submerged to the sea bed. The member
1 then either rests on the sea bed under the effect of gravity, or
(and as illustrated) is held by piles 100 driven through
passageways provided in the housing 1 and into the sea bed.
Preferably piling is effected by driving groups of piles by
hydraulic drive equipment generally of the type forming the subject
of Taylor Woodrow Construction Limited's U.S. Pat. No. 3,279,195 in
which in driving a group of piles load is taken from driven piles
of the group to a pile or piles being driven. In FIG. 1 the upright
column is referenced 2, the joint between the member 1 and the
column 2 is referenced 3, and the deck superstructure is referenced
2A.
Referring to FIGS. 2 and 3, in which a form of the member 1 is
shown in greater detail than in FIG. 1, the member 1 has defined
within it by walls 101 chambers for various purposes. The chambers
include chambers 102 for providing buoyancy and stability during
floatation and that are flooded for submerging; chambers 103 for
housing well heads 104 of subsea completions; chambers 105 for
housing plant and providing passageways for oil/gas flow ducts from
the subsea completions; a central chamber 106 from which the
chambers 105 radiate; and chambers 107 constituting galleries
giving access to anchorages of the tendons 4 of the joint 3.
The joint 3 includes tendons 4 which extend in four radially
spaced-apart groups (two of which are shown at 4A and 4B in FIG. 5)
from individual lower anchorages in a circular rib 108 on the upper
surface of the member 1, upwardly and inwardly to individual upper
anchorages around a circular base of a concrete vessel 109 (which,
in the form of FIGS. 4 and 5, replaces a socket member 6
illustrated in FIG. 1 and in which the column 2 is supported. This
arrangement of tendons permits limited rotation of the column 2
about its axis relative to the housing 1 of up to 10.degree. or
15.degree., and swinging movement, and also slight translational
and vertical movement of the column relative to the housing, these
various degrees of freedom permitting the joint between the column
and the housing to accommodate movement as a result of water
motion. The adoption of four groups of tendons gives a tendon
geometry such that no tendon is in line with a subsea completions
chamber 103, thus facilitating access to the lower tendon
anchorages from the galleries 107. The tendons are preferably of a
high strain capability synthetic plastics material.
The interior of the vessel 109 is connected to the central chamber
111 of the member 1 by a shaft 8' that is disposed centrally of the
tendons 4 and that passes through seal assemblies 9 and 10 between
the shaft and the vessel 109, and between the shaft and the member
1, respectively.
The top of the vessel 109 is formed as a socket 110 into which is
entered the bottom end of the column 2, which is also a prestressed
concrete. If desired there can be provision for oil storage within
the column 2.
In the form of FIGS. 2 and 3 the vessel 109 is of sufficient size
to permit drawing of the tendons 4 of the joint 3 into the interior
of the 109, whereby tendons can be replaced when desired. The form
of FIG. 1 is, in general, the same as that just described, except
that in the FIG. 1 form tendon replacement is carried out by
drawing the tendons into the member 1, which has tendon replacement
chambers 107A instead of the galleries 107 of the form of FIGS. 2
and 3. Access is gained to the tendon replacement chambers 107A via
suitable passageways.
FIG. 4 shows a modification of the form of FIG. 1, in which, in
addition to the tendon replacement chambers 107A in the housing 1,
an access gallery 111 to the upper tendon anchorages is provided in
a socket member 6A replacing the socket member 6.
Various arrangements can be utilized for effecting tendon
replacement, and these will now be described with reference to
FIGS. 5 to 23. For ease of description it will be assumed that a
tendon that is placed and tensioned to its operating load has to be
replaced.
The arrangement of FIGS. 5 to 8, which will be described first, is
suitable where access to the anchorages at each end of the tendon 4
is available (as illustrated in FIGS. 2 to 4). The tendon 4 is a
high strain capability synthetic plastics material, flared and
bonded at each end into a cylindrical steel member 123 or 124 that
is entered, at a mounting station, in a tubular portion 125 of a
tendon anchorage that terminates in a bulkhead 126. Each steel
member 123, 124 carries seals 127 co-operating with the anchorage
tubular portion 125, and there are provided in the tubular portion
125 further inflatable seals 128 that are normally deflated, but
that can be inflated in the event of failure of the seals 127. The
outer end of the steel member 123 at what is the lower end of the
tendon in FIGS. 2 to 4 is threaded and secured by a large nut 129
bearing via chocks (or shims) 130 on the adjacent anchorage
bulkhead 126; the other steel member 124 having a shoulder 124A
that bears (without the intervention of chocks) on its adjacent
bulkhead 126. There can thus be maintained a desired load in the
tendon. The shoulder 124A and the nut 129 are capped by sealing
domes (not shown) bolted to the bulkheads 126 and able to resist
full sea pressure in the event of failure of the seals 127,
equipment (not shown) being provided for detecting leakage into
these domes.
The tubular anchorage portions 12 terminate externally in fairleads
131 formed in the member 1 and the socket member 6.
Prior to effecting tendon replacement, the sealing domes are
removed and at the lower end of the tendon a cylindrical tendon
extension 132 is bolted to the outer end of the steel member 123. A
sealing cap 133 sufficiently large to accommodate the tendon
extension 132 is provided that can be fitted at the mounting
station at the end of the tendon by being bolted to the bulkhead
126 in place of the removed sealing dome.
At the mounting station at the upper end a shear key housing 134 is
fitted over the shoulder 124A and secured to the adjacent bulkhead
126, a piston head 135 is fitted to the outer end of the member
124, and a pressure bottle 136 is fitted to the shear key housing
134, taking the place of the removed sealing dome. The condition
now reached (including fitting of the extension 132 and cap 133
although in fact this is done later -- see below) is that
illustrated in FIG. 5 and in the upper half of FIG. 6.
By connecting pressurization equipment to an inlet 137 of the
bottle 136 the bottle 136 is pressurized to the external
hydrostatic pressure, the inflatable seals 128 if these have been
inflated being deflated as necessary to reduce frictional
resistance to tendon movements.
With the bottle 136 pressurized, and before placing the extension
132 and cap 133 in position, the nut 129 is detensioned utilizing a
prestressing jack, the chocks 130 released, and the nut removed
along with the chocks. During and after these operations sea
pressure maintains some pressure in the tendon and holds the member
123 in the tubular portion 125 whilst the extension 132 and the cap
133 are fitted.
Utilizing an inlet 138 the cap 133 is pressurized to equalize
pressure throughout the system and place the unit 4/123/124/132/135
in hydrostatic equilibrium, whereby by reducing the pressure in the
bottle 136 utilizing an outlet 139, which is the next operation,
this unit as a whole is drawn in the direction out of the cap 133
and into the bottle 136 so that the condition illustrated in FIG. 8
and in the lower half of FIG. 6 is reached. It is to be noted that
at the end of this movement the tendon extension 132 replaces the
member 124 in the upper tendon anchorage tubular portion 125, seals
140 carried by the extension 132 sealing on the tubular portion
125, so that the extension 132 replaces the member 124 in sealing
the tubular portion 125. As a precaution the inflatable seals 128
that are now able to co-operate with the extension 132 are inflated
and a double acting ram arrangement 141 (FIG. 7 is operated to
extend (lower half of Figure previously retracted (upper half of
FIG. 7) shear keys 142 so that they engage in an annular notch 143
(FIG. 6) in the extension 132. The extension 132 is thus locked in
position, sealing the tubular portion 125.
The bottle 136 is entirely de-pressurised and, utilizing previously
closed hatches (not shown) in the bottle 136 to gain access, the
member 123 is detached from the locked extension 132. The bottle
136 is then un-bolted from the shear key housing 134 and removed,
containing the tendon 4 with the members 123 and 124 and piston
head 135, which can then be taken out of the bottle.
To fit a new tendon, the piston head 135 is fitted to the member
124 of the new tendon and this tendon complete with the piston head
is inserted in the bottle 136. The bottle 136 is bolted to the
shear key housing 134 and the member 123 of the new tendon is
bolted to the extension 132 which has remained locked in
position.
The bottle 136 is pressurized, the inflated seals 128 are deflated,
the shear keys 142 are retracted, and the pressure in the bottle
136 is increased sufficiently above sea pressure to overcome the
resistance of seal friction etc., and move the unit
4/123/124/132/135 in the direction out of the bottle 136 and into
the cap 133. The cap 133 is depressurized and detached from it
bulkhead 126, the extension 132 is removed, the tendon is tensioned
and the nut 129 and chocks are fitted, the bottle 136, piston head
135 and shear key housing 134 are removed, and the sealing domes
are fitted. The extension 132, the cap 133, the shear key housing
134, the piston head 135 and the bottle 136 are then all available
for use in replacing another tendon of the joint.
The seals 127 and 140 can be replaced at each tendon replacement
operation, and can be of any convenient form.
It is to be noted that as the tendon being replaced is drawn out of
the lower anchorage and fairlead its end comes free. A light
articulating slide (not shown) may be provided to bridge the gap
between the lower and upper anchorages and provide a guide during
installation of the replacement tendon. As an alternative, the
tendon could be provided, throughout its length, with a washer
system offering several desirable facilities, including:
i. protection to the cable;
ii. means of centralizing the tendon whilst at the same time
allowing it to flex and bear in a controlled way against the
surfaces of the fairleads; and
iii. a member against which the tendon can be prestressed during
initial assembly so that it has sufficient rigidity at all times
when it is not under working load, this rigidity enabling the
tendon to be inserted into or withdrawn from the lower fairlead
without the need for a separate guide structure.
Such a washer system is illustrated in FIGS. 9, 10 and 11, in which
the individual washers of the system are referenced 144. Each is of
I-section as viewed on a radial plane and offers both to the tendon
4 and the fairlead 131 a convex surface 145 or 146. The washers 144
are placed in substantially abutting relationship along the tendon
4, and if torsional resistance is required neighbouring washers are
provided with inter-engaging male and female shear plates 147 and
148.
The arrangement of FIGS. 12 to 19, which will now be described, is
suitable where access for tendon removal is only possible to the
anchorage at one end of the tendon and no access at all is
available at the other end, the particular arrangement illustrated
being one in which the access is to the upper end of the tendon as
in FIG. 2. Where components as already described are utilized the
reference numerals already used are used also in FIGS. 12 to 19 and
the components will not be described again.
The principal differences in the form of FIGS. 12 to 19 are that
the tendon 4A has a central bore 150 through which a flexible drive
shaft can be passed; provision is made for prestressing and
chocking at the upper end utilizing a large nut 151 threaded onto
the member 124A and bearing via chocks 152 on the bulkhead 126; the
outer end of the member 124A and the piston head 135A that can be
attached thereto are bored out for receiving a drive unit for the
flexible drive shaft; at the lower end there is cast into the
member 1 a threaded anchor block 153; and the member 123A at this
end of the tendon carries a threaded anchor head 154 for engagement
with the anchor block 153 and to which the extension 132 is
bolted.
Tendon replacement is carried out as follows.
Working from the upper end, the tendon 4A is detensioned and the
chocks 152 and anchor nut 151 removed. The shear key housing 134 is
positioned and secured to the bulkhead 126. The piston head 135A is
secured to the member 124A, the flexible drive shaft is passed down
the bore 150 to engage the anchor head 154 and the drive unit for
this flexible drive shaft is mounted at the piston head end of the
member 124A. The bottle 136 is then pressurized and the drive unit
operated to unthread the anchor head 154 from the anchor block 153.
Once the anchor head is free of the anchor block the bottle 136 is
depressurized so that the unit 4A/123A/124A/132/135A is drawn in a
direction to enter the bottle 136 as already described, whereafter
operations as already described are carried out to enable the
bottle 136 containing the tendon 4A with the members 123A and 124A,
the piston head 135A, the flexible drive shaft and its drive unit,
and the anchor head 154 to be removed.
A new tendon is fitted substantially in the manner already
described but, of course, utilizing, in reverse, those operations
which are specific to the arrangement of FIGS. 12 to 19 and which
have just been described.
For locking the lower end of the tendon 4A against rotation whilst
the anchor head 154 is being unscrewed or screwed in, the member
123A is provided with spring-loaded splines 155 (FIG. 18) that
engage in a spline case 156 cast into the member 1. As an
alternative, illustrated in FIG. 19, spring loaded lugs 157 can be
provided in the member 1 for engagement with tapered splines 158
provided on the member 123A.
Coupling or uncoupling of the anchor head 154 can be achieved in
various other alternative ways, for example, by passing hydraulic
fluid through the bore in the tendon 4A under pressure to operate a
hydraulic motor arranged to rotate the anchor head with respect to
the tendon. As a further alternative, an actuator could be provided
at the upper end for rotating the entire tendon assembly to unscrew
it from the member 1. In this case the locking mechanisms of FIGS.
18 and 19 would not be used, and in order to transmit the torque
from the upper end to the housing it would be necessary to
incorporate the inter-engaging male and female shear plates 147 and
148 on the washers 144.
It is to be noted that in this form at the lower end, the tendon
extension 132 remains in position throughout the use of the tendon
in the joint, the extension 132 being disposed in a chamber 159 in
the member 1. This chamber 159 is substantially sealed but is
connected via a bleed duct 160 to the fairlead 131 to permit
equalization of pressure.
FIGS. 20 to 23 illustrate alternative arrangements that can be
provided, in the form of FIGS. 12 to 19 at the end of the tendon to
which direct access cannot be gained.
Referring first to FIGS. 20 and 22, the member 123B is fitted with
a circumferential key way 161 into which can engage a series of
spring-loaded keys 162 mounted in the member 1. When a tendon is
being fitted, these keys 162 are initially pushed out of the way,
the extension 132B provided in this form having a tapered end to
facilitate this operation. Eventually the spring-loading of the
keys is able to assert itself so that the keys 162 enter the key
ways 161 to lock the tendon against withdrawal.
When it is desired to effect withdrawal, oil is fed under pressure
down the bore in the tendon 4A and through a bore 163 in the member
123B to extend, radially of the member 123B, a number of rams 164
which thereby act on the keys 162 to urge the keys out of the key
way 161.
It is to be noted that the annular notch 143 in the extension 132B
has to be dimensioned such that the keys 162 will not enter it. As
a precautionary measure, radially-acting rams similar to the rams
164 can be provided in association with the notch 143.
In the form of FIGS. 21 and 23 the member 123C is provided with a
number of spring loaded arms 165 which are held against their
spring-loading by the extension (132) which is formed in this case
as a cap 66. In the member 1 there is provided an annular key way
167 for receiving the arms 165.
At the commencement of a tendon replacement operation, the cap 166
is fitted to the member 123C so that it is positioned as shown in
FIG. 21 with the skirt 166' of the cap 166 bearing on the arms 165
to hold them in their retracted positions. Retaining lugs 168 at
the skirt end of the cap 166 are disposed in slide ways 169 in the
member 123C to retain the cap on the member 123C. Tendon
replacement is then commenced substantially in the manner already
described with the cap 166 being maintained in its extended
position illustrated in FIG. 21 by pressure passed down the bore in
the tendon 4A and a bore 170 in the member 123C. Eventually the cap
166 impinges on the dead end 171 of the chamber 159 and the
pressure in the interior of the cap 166 is reduced to the
hydrostatic pressure so that the member 123C moves forward relative
to the cap 166 until the arms 165 become free from the cap skirt
166' and line up with apertures 172 in the cap, whereupon the arms
165 extend radially into the key way 167. The pressure at the
piston 135A end is then reduced to below hydrostatic pressure so
that the member 123C moves back until the extended arms 165 bear on
a frusto-conical bearing plate 173 forming one surface of the key
way 167. Operation is then proceeded with as already described.
To withdraw the tendon 4A it is necessary to retract the arms 165
from the key way 167. This is accomplished by driving the member
123C into the cap 166 by pressurizing the bottle 136 whilst the
pressure in the interior of the cap 166 remains at hydrostatic
pressure. If desired the pressure in the interior of the cap 166
can be reduced below hydrostatic pressure. As the member 123C moves
relative to the cap 166 the skirt 166' of the cap 166 acts on the
arms 165 to move to their retracted positions. The tendon is then
withdrawn by reducing the pressure in the bottle 136, thus allowing
sea water pressure to act on the exterior of the cap 166 to drive
the unit 4A/123C/124A/135A in the direction back into the bottle
136. The cap 166 is provided with an annular notch 143A that
corresponds to the notch 143 already described.
As a precaution, the facility is provided to reduce the pressure in
the interior of the cap 166 to atmospheric to ensure that there is
no possibility of the cap 166 releasing the arms 165 inadvertently
during withdrawal.
It is to be noted that in the form of FIGS. 21 and 23 (and also in
the case of FIGS. 20 and 22) there is no need to provide a sealing
cap or sealed cavity in the member 1. Disconnection of the cap 166
is accomplished by removing the retaining lugs 168 from the skirt
166' after opening normally-closed hatches in the bottle 136 and at
this stage the arms 165 are bolted in their retracted positions to
enable them to pass out of the cap 166. Further retraction of the
tendon to remove it fully from the cap 166 is achieved as
previously described by repressurizing the bottle 136 and then
reducing the pressure ahead of the piston 135A.
To sum up, during insertion the arms 165 are held retracted near
their tips by the skirt 166' of the cap 166 so that their initial
release occurs when the cap 166 impinges on the dead end 171.
During retraction of the tendon the arms 165 are brought back into
their retracted position and held there by the head of the cap 166.
It is, however, possible to operate without relying on impingement
of the cap 166 to establish anchorage. When operating in this way,
at the commencement the cap is fully closed onto the member 123C to
enshroud the arms 165, the cap being held in position by keeping
its interior at low pressure. At the end of the desired movement
the interior of the cap is pressurized above sea water pressure,
forcing the member 123C in the direction out of the cap until the
arms 165 are released through the apertures 172 to enter the key
way 167.
It is to be noted that the lugs 168 and their associated slide way
169 are provided as a precautionary measure to prevent loss of the
cap by, for example, incorrect operation of the hydraulic circuitry
of the arrangement, or snagging of the cap during withdrawal.
* * * * *